1. Field of the Invention
The present invention relates to deciphering the electromagnetically scattered echoes returned by obstacles in continuous media, and more particularly to a an apparatus for and a method of determining the geometry and material composition of a dielectric and/or conducting radar target by deciphering the backscattered signal returned from the target.
2. Description of the Prior Art
In the general field of electromagnetic backscattering, it is quite important and desirable to identify the composition of radar targets. This would allow the distinction between a real incoming target and a decoy, or once it is determined that the target is real, it would permit the distinction between various types of similar targets. Thus, it would become possible to classify target/obstacles as friendly or not. In either situation, the type or class of target/obstacle that returned the backscattered signals or echoes can be determined.
Heretofore, the prior art has analysed the electromagnetic echoes returned by targets of simple shapes. With few exceptions, the actual numerical calculations available in the prior art are sparse, pertain only to a few conductors, and rarely include penetration effects through dielectrics, or effects in the resonance region present beyond the low frequency (i.e., Rayleigh) spectral regime. Some of the prior art has attributed the rapid oscillations in cross-sectional values that are observed, to some sort of resonant phenomena; however, little or no effort has been made to actually cast the analysis into some explicit resonant form. In fact, the electromagnetic backscattering cross section of simple shaped targets, when plotted as function of frequency, exhibit so many rapid oscillations and complicated features that until the very recent teachings described in the present application, it did not appear possible to extract any physical information that may have been contained in them.
To predict the type of echo that a given target/obstacle will return when it is illuminated with a certain incident electromagnetic waveform is a direct scattering problem that has been "solved" in very few instances, i.e., for selected "separable" shapes, simple compositions, selected frequency ranges, etc. To extract physical information about a target/obstacle from the backscattered echos it has returned, and that has been somehow received and recorded, is an inverse scattering problem that has not been previously solved, as far as is known, even in the simplest of instances. Some theories and feasibility studies have been advanced but as far as is known, not even a simple flying gasfilled balloon has actually been identified by any scheme. A good present day radar system merely indicates how far the scattering target/obstacle is from the observer, and in which direction, provided the radar system is sensitive enough to pickup the returned signal, and sophisticated enough to pull it out of the ambient noise it comes buried into. No information is ever extracted about size, composition, shape, internal or external structures, weight, etc. of the scattering target/obstacle.